An experiment system of tubes with one weakly covered end was established, and the outfield characteristics of fuel vapor explosions were studied through experiments. The results are as follows. After the rupture of the weakly covered end, three outfield overpressure peaks appeared due to the rupture of the weakly covered end (P1), the venting of the flame (P2), and external explosion (P3). The value of overpressure peaks showed a downward trend with an increase in distance, and the maximum overpressure was formed due to the external explosion. The value of overpressure peaks were related to the L/D ratio of the tube. With an increase in the L/D ratio, P1 and P3 in the near field showed an upward linear trend, while P2 and P3 in the far field showed a quadratic trend. In the case of the same L/D ratio, the maximum overpressure largely depended on the fuel volume fraction and external distance. The flame shape showed a changing process of jet flame - radial tension - mushroom cloud-shaped flame. The mushroom-shaped flame was formed mainly due to the Kelvin-Helmholtz instability and vortex effect, and the value of axial flame parameters were greater than those of radial ones. With an increase in the L/D ratio, the axial flame parameters showed an upward linear trend, the radial flame parameters showed a downward linear trend, and their ratio showed an upward linear trend.